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2025 Questions QA
iimb-ugat
2025 Complete Paper Solution | QA
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Question 1.
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The value of an item depreciates $x\%$ per year. The present value of the item is $₹ 109350$. Its value after 3 years will be $₹ 79716.15$. Two years ago from now, its value, in rupees, was
A
13415.5
B
153000
C
132313.5
D
135000
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Text Explanation:
The value of an item depreciates $x\%$ per year. The present value is $₹ 109350$, and after 3 years it will be $₹ 79716.15$.
Using the depreciation formula:
$A = P\left(1 - \frac{x}{100}\right)^n$
where $A$ is the final value, $P$ is the initial value, $x$ is the rate of depreciation, and $n$ is the time in years.
$79716.15 = 109350 \left(1 - \frac{x}{100}\right)^3$
$\left(1 - \frac{x}{100}\right)^3 = \frac{79716.15}{109350}$
$\left(1 - \frac{x}{100}\right)^3 = \frac{7971615}{10935000}$
$\left(1 - \frac{x}{100}\right)^3 = \frac{729}{1000}$
Taking the cube root:
$1 - \frac{x}{100} = \sqrt[3]{\frac{729}{1000}}$
$1 - \frac{x}{100} = \frac{9}{10}$
$1 - \frac{x}{100} = 0.9$
Let the value of the item 2 years ago be $V$. The present value is the result of depreciating $V$ for 2 years:
$109350 = V (0.9)^2$
$109350 = V (0.81)$
$V = \frac{109350}{0.81}$
$V = \frac{10935000}{81}$
$V = 135000$
The value of the item 2 years ago was $₹ 135000$.
Question 2.
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The slope of the tangent to the curve $y = x^2 - 4\cos x$, $x \in [0, \pi]$ is maximum when $x$ is equal to
A
$\frac{\pi}{3}$
B
0
C
$\frac{5\pi}{6}$
D
$\frac{2\pi}{3}$
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Text Explanation:
Let the equation of the curve be $y = f(x)$.
$y = x^2 - 4\cos x$
The slope of the tangent to the curve at any point $x$ is given by the first derivative, $\frac{dy}{dx}$. Let the slope be denoted by $m$.
$m = \frac{dy}{dx}$
$m = \frac{d}{dx}(x^2 - 4\cos x)$
$m = 2x - 4(-\sin x)$
$m = 2x + 4\sin x$
To maximize this function $m$ on the interval $[0, \pi]$, differentiate $m$ with respect to $x$ and equate it to zero.
$\frac{dm}{dx} = \frac{d}{dx}(2x + 4\sin x)$
$\frac{dm}{dx} = 2 + 4\cos x$
Setting $\frac{dm}{dx} = 0$ for critical points:
$2 + 4\cos x = 0$
$4\cos x = -2$
$\cos x = -\frac{1}{2}$
Finding $x$ in the interval $[0, \pi]$ such that $\cos x = -\frac{1}{2}$:
Since $\cos x$ is negative, $x$ must be in the second quadrant.
Given that $\cos(\frac{\pi}{3}) = \frac{1}{2}$:
$x = \pi - \frac{\pi}{3}$
$x = \frac{2\pi}{3}$
To confirm that this value of $x$ gives a maximum slope, find the second derivative of $m$:
$\frac{d^2m}{dx^2} = \frac{d}{dx}(2 + 4\cos x)$
$\frac{d^2m}{dx^2} = -4\sin x$
Evaluating at $x = \frac{2\pi}{3}$:
$\frac{d^2m}{dx^2}\bigg|_{x=\frac{2\pi}{3}} = -4\sin\left(\frac{2\pi}{3}\right)$
$\frac{d^2m}{dx^2}\bigg|_{x=\frac{2\pi}{3}} = -4\left(\frac{\sqrt{3}}{2}\right)$
$\frac{d^2m}{dx^2}\bigg|_{x=\frac{2\pi}{3}} = -2\sqrt{3}$
Since the second derivative is negative ($< 0$), the slope $m$ is at a local maximum at $x = \frac{2\pi}{3}$.
Checking the endpoints of the interval $[0, \pi]$ to ensure it is the global maximum:
At $x = 0$:
$m = 2(0) + 4\sin(0)$
$m = 0$
At $x = \pi$:
$m = 2\pi + 4\sin(\pi)$
$m = 2\pi \approx 6.28$
At $x = \frac{2\pi}{3}$:
$m = 2\left(\frac{2\pi}{3}\right) + 4\left(\frac{\sqrt{3}}{2}\right)$
$m = \frac{4\pi}{3} + 2\sqrt{3} \approx 7.65$
The value at $x = \frac{2\pi}{3}$ is the highest.
Therefore, the slope of the tangent to the curve is maximum when $x = \frac{2\pi}{3}$.
Question 3.
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Let $f(x) = \tan^{-1}\left(\sqrt{\frac{1-\cos x}{1+\cos x}}\right)$; $x \in (0,\pi)$. A normal to $y = f(x)$ at $x = \frac{\pi}{3}$ passes through the point:
A
$\left(\frac{\pi}{3}, \frac{\pi}{2}\right)$
B
$\left(\frac{\pi}{3}, 0\right)$
C
$(0, 0)$
D
$\left(\frac{\pi}{3}, \frac{\pi}{6}\right)$
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Text Explanation:
Simplify the expression inside the inverse tangent using half-angle trigonometric identities:
$1 - \cos x = 2\sin^2\left(\frac{x}{2}\right)$
$1 + \cos x = 2\cos^2\left(\frac{x}{2}\right)$
Substitute these into the function:
$f(x) = \tan^{-1}\left(\sqrt{\frac{2\sin^2(x/2)}{2\cos^2(x/2)}}\right)$
$f(x) = \tan^{-1}\left(\sqrt{\tan^2\left(\frac{x}{2}\right)}\right)$
$f(x) = \tan^{-1}\left(\left|\tan\left(\frac{x}{2}\right)\right|\right)$
Since $x \in (0, \pi)$, the half-angle $\frac{x}{2} \in (0, \frac{\pi}{2})$. In this interval, $\tan(\frac{x}{2})$ is positive, so $|\tan(\frac{x}{2})| = \tan(\frac{x}{2})$.
$f(x) = \tan^{-1}\left(\tan\left(\frac{x}{2}\right)\right)$
$f(x) = \frac{x}{2}$
The normal is at $x = \frac{\pi}{3}$. The $y$-coordinate at this point:
$y = f\left(\frac{\pi}{3}\right)$
$y = \frac{\pi/3}{2}$
$y = \frac{\pi}{6}$
The point of tangency is $\left(\frac{\pi}{3}, \frac{\pi}{6}\right)$.
The derivative of the simplified function $f(x) = \frac{x}{2}$:
$f'(x) = \frac{1}{2}$
This is the slope of the tangent. The slope of the normal is the negative reciprocal of the tangent slope:
$m_n = -\frac{1}{1/2}$
$m_n = -2$
Using the point-slope form with point $\left(\frac{\pi}{3}, \frac{\pi}{6}\right)$ and slope $-2$:
$y - \frac{\pi}{6} = -2\left(x - \frac{\pi}{3}\right)$
$y - \frac{\pi}{6} = -2x + \frac{2\pi}{3}$
$2x + y = \frac{2\pi}{3} + \frac{\pi}{6}$
$2x + y = \frac{4\pi + \pi}{6}$
$2x + y = \frac{5\pi}{6}$
Check which of the given points satisfies the equation $2x + y = \frac{5\pi}{6}$:
Option 1: $\left(\frac{\pi}{3}, \frac{\pi}{2}\right)$
$2\left(\frac{\pi}{3}\right) + \frac{\pi}{2} = \frac{7\pi}{6} \neq \frac{5\pi}{6}$
Option 2: $\left(\frac{\pi}{3}, 0\right)$
$2\left(\frac{\pi}{3}\right) + 0 = \frac{4\pi}{6} \neq \frac{5\pi}{6}$
Option 3: $(0, 0)$
$0 + 0 = 0 \neq \frac{5\pi}{6}$
Option 4: $\left(\frac{\pi}{3}, \frac{\pi}{6}\right)$
$2\left(\frac{\pi}{3}\right) + \frac{\pi}{6} = \frac{4\pi}{6} + \frac{\pi}{6} = \frac{5\pi}{6}$ ✓
Therefore, the normal passes through the point $\left(\frac{\pi}{3}, \frac{\pi}{6}\right)$.
Question 4.
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Let $A \times B$ denote the Cartesian product of sets $A$ and $B$. If the cardinality of $A \cap B$ is $10$, then the cardinality of $(A \times B) \cap (B \times A)$ is:
A
$2^{10}$
B
$10$
C
$100$
D
None of these options
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Text Explanation:
The standard property of set theory states that for any sets $A, B, C,$ and $D$:
$(A \times B) \cap (C \times D) = (A \cap C) \times (B \cap D)$
In this case, replacing $C$ with $B$ and $D$ with $A$:
$(A \times B) \cap (B \times A) = (A \cap B) \times (B \cap A)$
The intersection of sets is commutative, meaning $A \cap B = B \cap A$.
Therefore:
$(A \times B) \cap (B \times A) = (A \cap B) \times (A \cap B)$
The cardinality of a Cartesian product $X \times Y$ is the product of the cardinalities of the individual sets:
$n(X \times Y) = n(X) \times n(Y)$
Applying this to the simplified expression:
$n((A \times B) \cap (B \times A)) = n((A \cap B) \times (A \cap B))$
$n((A \times B) \cap (B \times A)) = n(A \cap B) \times n(A \cap B)$
$n((A \times B) \cap (B \times A)) = [n(A \cap B)]^2$
Given that $n(A \cap B) = 10$:
$n((A \times B) \cap (B \times A)) = 10 \times 10$
$n((A \times B) \cap (B \times A)) = 100$
Therefore, the cardinality of $(A \times B) \cap (B \times A)$ is $100$.
Question 5.
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Let $f(x) = \left|\frac{x}{2}\right|$ and $g(x) = \sqrt{3}\cos x + \sin x - 1$, for all real numbers $x$. If $[ \ \ ]$ denotes the greatest integer function, then the range of the function $[f \circ g]$ is:
A
$\{0, 1\}$
B
$\{-1, 0, 1\}$
C
$\{0\}$
D
$\{1\}$
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Text Explanation:
The function is $g(x) = (\sqrt{3}\cos x + \sin x) - 1$.
The expression $a\cos x + b\sin x$ ranges from $-\sqrt{a^2+b^2}$ to $\sqrt{a^2+b^2}$.
Here, $a = \sqrt{3}$ and $b = 1$.
Maximum value $= \sqrt{(\sqrt{3})^2 + 1^2}$
$= \sqrt{3+1}$
$= 2$
Minimum value $= -2$
So, the range of $(\sqrt{3}\cos x + \sin x)$ is $[-2, 2]$.
Therefore, the range of $g(x)$ is $[-2 - 1, 2 - 1]$, which simplifies to $[-3, 1]$.
Let $u = g(x)$, so $u \in [-3, 1]$.
The function becomes $f(u) = \left|\frac{u}{2}\right|$.
Analyzing the values of $f(u)$ as $u$ varies from $-3$ to $1$:
If $u = -3$, $f(-3) = |-1.5| = 1.5$ (Maximum value)
If $u = 0$, $f(0) = 0$ (Minimum value)
If $u = 1$, $f(1) = 0.5$
The range of the composite function $(f \circ g)(x)$ is continuous from the minimum to the maximum, which is $[0, 1.5]$.
For any value $y$ in the interval $[0, 1.5]$, the greatest integer function gives:
For $y \in [0, 1)$, $[y] = 0$
For $y \in [1, 1.5]$, $[y] = 1$
Thus, the possible output values are only the integers $0$ and $1$.
Therefore, the range is $\{0, 1\}$.
Question 6.
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The perimeters of a regular hexagon and a regular octagon are equal. Find the ratio of the area of the octagon to that of the hexagon. [Use $\tan 67.5° = (\sqrt{2} + 1)$]
A
$\frac{\sqrt{6} + \sqrt{2}}{4}$
B
$\frac{\sqrt{6} + \sqrt{3}}{3}$
C
$\frac{\sqrt{6} + \sqrt{2}}{2}$
D
$\frac{\sqrt{6} + \sqrt{3}}{4}$
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Text Explanation:
Perimeter of a regular hexagon = Perimeter of a regular octagon.
Value to use: $\tan 67.5^\circ = (\sqrt{2} + 1)$.
Let the side length of the regular hexagon be $a$ and the side length of the regular octagon be $b$.
Since their perimeters are equal:
$6a = 8b$
$a = \frac{8b}{6}$
$a = \frac{4b}{3}$
The area of a regular hexagon with side $a$ is given by:
$A_H = \frac{3\sqrt{3}}{2} a^2$
Substituting $a = \frac{4b}{3}$:
$A_H = \frac{3\sqrt{3}}{2} \left( \frac{4b}{3} \right)^2$
$A_H = \frac{3\sqrt{3}}{2} \times \frac{16b^2}{9}$
$A_H = \frac{8\sqrt{3}}{3} b^2$
A regular octagon can be divided into 8 congruent isosceles triangles with the center of the octagon as the common vertex.
Base of each triangle = side of octagon = $b$
Central angle = $\frac{360^\circ}{8} = 45^\circ$
Base angles of the triangle = $\frac{180^\circ - 45^\circ}{2} = 67.5^\circ$
Let $h$ be the height (apothem) of one such triangle.
Using trigonometry in the right-angled half of the triangle:
$\tan 67.5^\circ = \frac{h}{(b/2)}$
$h = \frac{b}{2} \tan 67.5^\circ$
Area of one triangle:
$= \frac{1}{2} \times b \times \frac{b}{2} \tan 67.5^\circ$
$= \frac{b^2}{4} \tan 67.5^\circ$
Total Area of Octagon:
$A_O = 8 \times \frac{b^2}{4} \tan 67.5^\circ$
$A_O = 2b^2 \tan 67.5^\circ$
Using $\tan 67.5^\circ = (\sqrt{2} + 1)$:
$A_O = 2b^2 (\sqrt{2} + 1)$
The ratio $\frac{A_O}{A_H}$:
$\text{Ratio} = \frac{2b^2(\sqrt{2} + 1)}{\frac{8\sqrt{3}}{3}b^2}$
$\text{Ratio} = \frac{2(\sqrt{2} + 1) \times 3}{8\sqrt{3}}$
$\text{Ratio} = \frac{6(\sqrt{2} + 1)}{8\sqrt{3}}$
$\text{Ratio} = \frac{3(\sqrt{2} + 1)}{4\sqrt{3}}$
Rationalizing the denominator:
$\text{Ratio} = \frac{3\sqrt{3}(\sqrt{2} + 1)}{4 \times 3}$
$\text{Ratio} = \frac{\sqrt{3}(\sqrt{2} + 1)}{4}$
$\text{Ratio} = \frac{\sqrt{6} + \sqrt{3}}{4}$
Instructions
Consider the data of four schools (S1, S2, S3, S4) in a city in this table below:
School
Number of Students
Percentage of Boys
IX
X
XI
XII
IX
X
XI
XII
S1
120
90
150
125
40
30
60
80
S2
150
100
120
100
30
55
50
45
S3
140
120
100
120
20
40
65
60
S4
100
100
80
150
35
45
80
40
Question 7.
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The number of girls in XI in the school S3 is approximately ______% of the number of boys in IX in the school S2.
A
77.87
B
88.87
C
77.78
D
88.78
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Text Explanation:
The relevant data from the table:
School
Class
Total Students
% of Boys
% of Girls
S3
XI
100
65%
$100 - 65 = 35\%$
S2
IX
150
30%
—
The number of girls in School S3 (Class XI):
$\text{Girls}$
$= \text{Total Students} \times (\% \text{ Girls})$
$= 100 \times 35\%$
$= 100 \times 0.35$
$= 35$
The number of boys in School S2 (Class IX):
$\text{Boys}$
$= \text{Total Students} \times (\% \text{ Boys})$
$= 150 \times 30\%$
$= 150 \times 0.30$
$= 45$
The percentage that the number of girls in S3 (Class XI) represents of the number of boys in S2 (Class IX):
$\text{Percentage}$
$= \left( \frac{\text{Girls (S3, XI)}}{\text{Boys (S2, IX)}} \right) \times 100$
$= \left( \frac{35}{45} \right) \times 100$
$= \frac{7}{9} \times 100$
$\approx 77.78\%$
Therefore, the answer is 77.78 (Option 3).
Question 8.
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In class XII, the number of girls in the school ______ is more than the combined number of girls in the school ______ and ______.
A
S4, S1, S2
B
S2, S1, S4
C
S2, S1, S3
D
S4, S2, S3
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Text Explanation:
Calculate the number of girls in Class XII for all schools to satisfy the condition:
$\text{Girls}(A) > \text{Girls}(B) + \text{Girls}(C)$
Using the formula: $\text{Girls} = \text{Total} \times (100\% - \% \text{Boys})$
School
Total Students (XII)
% Boys
% Girls
Calculation
No. of Girls
S1
125
80%
20%
$125 \times 0.20$
25
S2
100
45%
55%
$100 \times 0.55$
55
S3
120
60%
40%
$120 \times 0.40$
48
S4
150
40%
60%
$150 \times 0.60$
90
Checking each option to find where the first school has more girls than the sum of the other two:
Option 1: S4, S1, S2
$\text{Girls}(S4) > \text{Girls}(S1) + \text{Girls}(S2)$
$90 > 25 + 55$
$90 > 80$
This is TRUE.
Option 2: S2, S1, S4
$55 > 25 + 90$
$55 > 115$
This is FALSE.
Option 3: S2, S1, S3
$55 > 25 + 48$
$55 > 73$
This is FALSE.
Option 4: S4, S2, S3
$90 > 55 + 48$
$90 > 103$
This is FALSE.
Therefore, the answer is Option 1: S4, S1, S2.
Question 9.
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For all schools, the correct arrangement of classes in ascending order of number of boys is ______.
A
IX, X, XI, XII
B
IX, X, XII, XI
C
X, IX, XI, XII
D
X, IX, XII, XI
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Text Explanation:
The number of boys for each school is calculated by multiplying the Total Students by the Percentage of Boys.
School
Class IX Boys
Class X Boys
Class XI Boys
Class XII Boys
S1
$120 \times 40\% = 48$
$90 \times 30\% = 27$
$150 \times 60\% = 90$
$125 \times 80\% = 100$
S2
$150 \times 30\% = 45$
$100 \times 55\% = 55$
$120 \times 50\% = 60$
$100 \times 45\% = 45$
S3
$140 \times 20\% = 28$
$120 \times 40\% = 48$
$100 \times 65\% = 65$
$120 \times 60\% = 72$
S4
$100 \times 35\% = 35$
$100 \times 45\% = 45$
$80 \times 80\% = 64$
$150 \times 40\% = 60$
TOTAL
156
175
279
277
The total number of boys in each class across all schools:
Class IX: $156$
Class X: $175$
Class XI: $279$
Class XII: $277$
Arranging the classes from lowest to highest:
$156 < 175 < 277 < 279$
The correct arrangement is IX, X, XII, XI.
Question 10.
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On arranging schools in descending order of total number of girls in all classes, the correct order is ______.
A
S2, S3, S1, S4
B
S2, S3, S4, S1
C
S3, S2, S1, S4
D
S3, S2, S4, S1
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Text Explanation:
Since the table gives the percentage of boys, the percentage of girls is calculated as:
$\% \text{Girls} = 100\% - \% \text{Boys}$
The number of girls for each class is calculated using:
$\text{Number of Girls} = \text{Total Students} \times \% \text{Girls}$
The table below breaks down the calculation for each class and sums the total girls for every school.
School
Class IX
Class X
Class XI
Class XII
Total Girls
S1
$120 \times 60\% = 72$
$90 \times 70\% = 63$
$150 \times 40\% = 60$
$125 \times 20\% = 25$
220
S2
$150 \times 70\% = 105$
$100 \times 45\% = 45$
$120 \times 50\% = 60$
$100 \times 55\% = 55$
265
S3
$140 \times 80\% = 112$
$120 \times 60\% = 72$
$100 \times 35\% = 35$
$120 \times 40\% = 48$
267
S4
$100 \times 65\% = 65$
$100 \times 55\% = 55$
$80 \times 20\% = 16$
$150 \times 60\% = 90$
226
Arranging the schools from the highest number of girls to the lowest:
S3: 267
S2: 265
S4: 226
S1: 220
Therefore, the descending order is: $S3, S2, S4, S1$
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